Mattress system

ABSTRACT

There is described a mattress system ( 20 ) comprising a mattress, an airflow driving device ( 14 ) and a heat adjustment unit ( 28 ). The mattress has a mattress cover ( 24 ) enclosing an internal mattress ( 10 ) such that a mattress air chamber is formed between the internal mattress and the mattress cover. The airflow driving device is in fluid communication with the mattress air chamber via an air chamber inlet and an air chamber outlet. The airflow driving device is operable to drive an airflow through the mattress air chamber from the air chamber inlet to the air chamber outlet. The heat adjustment unit is for heating or cooling the airflow so as to control a temperature of the airflow within the mattress air chamber. There is also described a mattress. In addition, there is described an apparatus for providing a temperature-controlled airflow through a mattress air chamber connected to the apparatus.

CROSS-REFERENCED TO RELATED APPLICATION(S)

This application is a National Phase Patent Application of InternationalApplication Number PCT/GB2009/000596, filed on Mar. 4, 2009, whichclaims priority to and the benefit of GB Application No. 0805796.0,filed Mar. 31, 2008

FIELD OF THE INVENTION

The present invention relates to a mattress system. The invention alsorelates to the mattress itself and to an apparatus for providing atemperature-controlled airflow through a mattress air chamber connectedto the apparatus.

Although the invention is primarily concerned with inflatable mattressesto provide yielding support for a recumbent human body, as used hereinthe term “mattress” is intended to include resilient cushions, seats andlike body-support structures. Furthermore, a mattress according to theinvention may be used to support any form of load, including loads otherthan a human body.

BACKGROUND OF THE INVENTION

Surgical patients undergoing major procedures and general anaesthesiaface several consequences during and following the operation. Keepingthe body temperature of a patient within normal limits is an importantgoal while in the operating room. Likewise, prevention of post-operativepressure ulcers requires addressing the patient's skin pressures duringtheir immobilised state.

There are currently products available to provide warming to patientswho are undergoing surgery and who are under anaesthesia. These havelimitations to the surgeon and patient.

One type of conventional heater system which is currently available issimilar to a normal electric-blanket for a bed. Such heater systems areplaced under the patient between the patient and the mattress to allowfor an efficient heat transfer. However, these systems are notcompatible with the use of dynamic pressure-relieving mattress systemssuch as the Talley Quattro range of products available from Talley GroupLimited of Abbey Park Industrial Estate, Premier Way, Romsey, HampshireSO51 9DQ, United Kingdom.

Dynamic pressure-relieving mattress systems of this kind are intended toalleviate the possibility of pressure sores by having an inflatablemattress with a number of separate inflation chambers that areinflatable independently of one another to a desired inflation pressure.Generally, each inflation chamber includes a respective plurality ofmutually spaced inflatable cells. For example, FIG. 1 is a schematicrepresentation of such an inflatable mattress 10 including a number ofinflation cells 12 which are arranged to form four separate inflationchambers 12 a, 12 b, 12 c and 12 d. The inflatable mattress 10 iselongate in direction y. The inflation cells 12 are each elongate inorthogonal direction x and are arranged side by side (at different ycoordinates) so as to extend widthways across the mattress 10.

In use, a pump and control unit 14 is connected to the mattress 10 viafour separate air hoses 16 a, 16 b, 16 c and 16 d. In FIG. 1, hoses 16 aand 16 b are schematically shown as solid lines and hoses 16 c and 16 dare schematically shown as dashed lines. The hoses 16 are used toindependently vary the inflation pressure of each inflation chamber overtime. For example, in a particular mode of operation, the second, thirdand fourth inflation chambers 12 b, 12 c and 12 d will initially beinflated, with a reduced pressure in the inflation cells of the firstinflation chamber 12 a. After a specified time period, the configurationwill change such that the first inflation chamber 12 a will be inflatedand the pressure in the second inflation chamber 12 b will be reduced.Next, the second inflation chamber 12 b will be inflated and thepressure in the third inflation chamber 12 c will be reduced. And,finally, the third inflation chamber 12 c will be inflated and thepressure in the fourth inflation chamber 12 d will be reduced. The pumpand control unit 14 continually cycles through these four configurationssuch that, at any given time, the patient is only supported by 75% ofthe load-bearing upper surface of the mattress 10. This helps to preventpressure sores by relieving interface pressure against a patient's softtissue when immobilized for extended time periods, for instance duringextended surgical operation procedures. Further details regardingdynamic pressure-relieving mattress systems are given in EP 0,732,886 inthe name of Talley Group Limited.

The conventional electric-blanket-like heater systems mentioned aboveare not suitable for use with dynamic pressure-relieving mattresssystems because the contact surface between the patient and the mattressis modified from being a stretch material (of the dynamicpressure-relieving mattress) to a non-stretch material or material withreduced-stretch characteristics (of the heater system). Therefore longsurgical procedures (which could be as long as 20 hours) can cause theonset of serious pressure sores as the patient is immobilised for such along period.

Other heater systems are known in which a light gown or cover is placedover the patient, and warm air is blown over the patient beneath theoverlying cover or gown. Such heater systems only allow warming of thepatient from their top side and limit the accessibility of the patientto the surgeon.

The present invention seeks to provide an alternative system whichprovides various advantages over those of the prior art. In particular,the present invention aims to provide an effective patient heatingsystem which is compatible with the use of a dynamic pressure-relievingmattress system.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda mattress system comprising a mattress having a mattress coverenclosing an internal mattress such that a mattress air chamber isformed between the internal mattress and the mattress cover. Themattress system further comprises an airflow driving device in fluidcommunication with the mattress air chamber via an air chamber inlet andan air chamber outlet. The airflow driving device is operable to drivean airflow through the mattress air chamber from the air chamber inletto the air chamber outlet. Also, the mattress system comprises a heatadjustment unit for heating or cooling the airflow so as to control atemperature of the airflow within the mattress air chamber.

Such a mattress system provides an effective way of heating a patientfrom beneath during an operation, for example. Furthermore, access tothe patient by the surgeon is not compromised. Also, since thetemperature-conditioned airflow does not contact the patient lying onthe mattress, infection risk and unwanted airflows around the patientare both reduced.

In addition, the mattress system of the present invention is suitablefor use with a dynamic-pressure-relieving mattress without compromisingthe effectiveness of the pressure-relieving therapy. The use of thissystem is therefore intended for patients who may be a high risk forhypothermia during surgery and/or for pressure ulcers post-operatively.

The heat adjustment unit may comprise a heater for heating the airflowand/or an air-conditioning unit and/or a refrigeration unit for coolingthe airflow.

The airflow driving device may comprise a fan or an air pump, forexample. Although the terms “air and “airflow” have been used in theclaims and the description, it will be appreciated that gases other thanair may be suitable for use in the present invention.

Advantageously, the mattress system further comprises an air inletconduit extending within the mattress air chamber from the air chamberinlet. The air inlet conduit comprises a plurality of mutually spacedholes for introducing the temperature-controlled airflow into themattress air chamber at a plurality of locations.

In one embodiment, the air inlet conduit and the holes are arranged(e.g. in size and location) to provide a substantially constanttemperature distribution of the airflow within the mattress air chamber.In an alternative embodiment, the mattress is elongate and the air inletconduit and the holes are arranged (e.g. in size and location) toprovide a temperature distribution of the airflow within the mattressair chamber which varies along the length of the mattress.

Optionally, the mattress is elongate and the air chamber inlet islocated at or near a first corner of the mattress such that the airinlet conduit extends along a longitudinal edge of the mattress towardsa second corner of the mattress. In one embodiment, the air inletconduit further extends from the second corner of the mattress along awidthwise edge of the mattress towards a third corner of the mattressand then partially extends back along the opposite longitudinal edge ofthe mattress towards the fourth corner of the mattress.

Advantageously, the mattress system further comprises an air outletconduit extending within the mattress air chamber to the air chamberoutlet. The air outlet conduit comprises at least one hole for conveyingthe temperature-controlled airflow out of the mattress air chamber. Inone embodiment, the air chamber outlet is located at or near the fourthcorner of the mattress and the air outlet conduit extends approximatelyone third of the way along the longitudinal edge of the mattress towardsthe third corner of the mattress.

Advantageously, the mattress system further comprises a temperaturesensor arranged to sense a temperature of the airflow. In oneembodiment, the temperature sensor comprises a first temperature sensorarranged to sense a temperature of a first airflow from the heatadjustment unit to the air chamber inlet. Alternatively/additionally,the temperature sensor comprises a return temperature sensor arranged tosense a temperature of a return airflow from the air chamber outlet tothe heat adjustment unit.

Advantageously, the mattress system further comprises a processoroperable to control the heat adjustment unit based on the sensed airflowtemperature. More advantageously, the mattress system further comprisesmeans for selecting a desired temperature distribution of the airflowwithin the mattress air chamber. In this embodiment, the processor isfurther operable to control the heat adjustment unit based on theselected temperature distribution.

Advantageously, the internal mattress is an inflatable mattress. In oneembodiment, the inflatable mattress comprises at least two separateinflation chambers that are inflatable independently of one another to adesired inflation pressure. Alternatively/additionally, each inflationchamber comprises a respective plurality of mutually spaced inflatablecells. A pump and a control system may be provided that are togetheroperable to independently vary the inflation pressure of each inflationchamber over time.

The mattress has a load-bearing upper surface for receiving a load.Advantageously, the lower surface of the mattress comprises aninsulating layer.

Advantageously, the mattress is radiolucent.

According to a second aspect of the present invention, there is provideda mattress comprising an internal mattress. A mattress cover enclosesthe internal mattress such that a mattress air chamber is formed betweenthe internal mattress and the mattress cover. The mattress covercomprises an air chamber inlet and an air chamber outlet arranged toallow a temperature-controlled airflow to pass through the mattress airchamber from the air chamber inlet to the air chamber outlet. An airinlet conduit extends within the mattress air chamber from the airchamber inlet. The air inlet conduit comprises a plurality of mutuallyspaced holes for introducing the temperature-controlled airflow into themattress air chamber at a plurality of locations. An air outlet conduitextends within the mattress air chamber to the air chamber outlet. Theair outlet conduit comprises at least one hole for conveying thetemperature-controlled airflow out of the mattress air chamber.

According to a third aspect of the present invention, there is providedan apparatus for providing a temperature-controlled airflow through amattress air chamber connected to the apparatus. The apparatuscomprises: an air outlet for provision of a first airflow from theapparatus to the connected mattress air chamber; an air inlet forreceiving a return airflow from the connected mattress air chamber tothe apparatus; an airflow driving device for driving an airflow from theair inlet towards the air outlet so as to drive the first and returnairflows; a heat adjustment unit for heating or cooling the airflow; afirst temperature sensor arranged to sense a temperature of the firstairflow; a return temperature sensor arranged to sense a temperature ofthe return airflow; and a processor operable to control the heatadjustment unit based on the sensed first airflow temperature, thesensed return airflow temperature and a pre-selected desired temperaturedistribution of the airflow within the mattress air chamber.

Other preferred features of the present invention are set out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of a known dynamicpressure-relieving mattress system;

FIG. 2 is a perspective view of a mattress system in accordance with apreferred embodiment of the present invention;

FIG. 2 a is a perspective view of the mattress system of FIG. 2 with theinternal mattress not shown;

FIG. 3 is a schematic representation of a heater-blower unit used in theembodiment of FIG. 2; and

FIG. 4 is a schematic plan view of a mattress used in the embodiment ofFIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A preferred embodiment of a mattress system 20 in accordance with thepresent invention is shown in FIG. 2. This example is an operating roomapplication where a temperature in the range 25 to 40° C. is typicallyrequired at the load-bearing mattress surface.

The mattress system 20 in FIG. 2 comprises a mattress 22 having amattress cover 24 enclosing an internal inflatable mattress 10. Betweenthe internal inflatable mattress 10 and the mattress cover 24 there is amattress air chamber 30. The mattress air chamber 30 is not clearlyshown in FIG. 2, but it can be seen in the schematic plan view of FIG.4, described below. Furthermore, the mattress system 20 is also depictedin FIG. 2 a without the internal inflatable mattress 10 so that othercomponents can be more clearly seen.

In the preferred embodiment of FIG. 2, the internal inflatable mattressis a dynamic pressure-relieving mattress 10 as described above withreference to FIG. 1. The internal inflatable mattress 10 is connected toits associated pump and control unit 14 by means of a flexible conduit26. The flexible conduit 26 encloses the four air hoses 16 a, 16 b, 16 cand 16 d for inflating and deflating the four separate inflationchambers 12 a, 12 b, 12 c and 12 d of the internal inflatable mattress10.

The mattress system 20 further comprises a heater-blower unit 28connected to the mattress air chamber 30 by means of inlet and outlethoses 32 a and 32 b. In this embodiment, the heater-blower unit isdisposed outside the mattress. The system is able to provide atemperature-controlled airflow through the air chamber 30 by means ofthe heater-blower unit 28. The heater-blower unit 28 of the mattresssystem 20 will now be described in more detail with reference to FIG. 3.

The heater-blower unit 28 has a housing 46 through which there is an airpassageway 48 which runs between an air inlet 49 b and an air outlet 49a of the housing 46. The air passageway contains a fan 50, a heater 52and two temperature sensors 54 and 56. The fan 50 and the heater 52 areeach disposed between the air inlet 49 b and the air outlet 49 a. Theheater 52 is in fact disposed between the fan 50 and the air outlet 49a.

The heater-blower unit also includes a processor 58, a display 60 and acontrol panel 62. The fan 50, the heater 52, the temperature sensors 54and 56, the display 60 and the control panel 62 are all coupled to theprocessor as shown by the dashed lines in FIG. 3.

In use, the air outlet 49 a is connected to the inlet hose 32 a of themattress air chamber 30. Similarly, the air inlet 49 b is connected tothe outlet hose 32 b of the mattress air chamber 30. The fan 50 acts todrive an airflow in the direction shown by arrow 64 from the air inlet49 a towards the air outlet 49 b. Thus, the fan 50 drives an airflow outof the air passageway 48 of the heater-blower unit 28 via the air outlet49 a. The airflow is then driven through the hose 32 a into the mattressair chamber 30. Having passed through the mattress air chamber 30, theairflow is driven through the hose 32 b and back into the air passageway48 of the heater-blower unit via the air inlet 49 b. Thus, a continuouscirculation of air is provided between the heater-blower unit and theconnected mattress air chamber 30. The airflow driven by the fan 50 is anon-pressurised airflow. Thus, there is no pressurised cushion of airformed within the mattress air chamber 30. This ensures that any therapyprovided by the internal pressure-relieving mattress 10 is notcompromised since the patient's bodyweight is effectively supported bythe internal mattress 10 rather than by the mattress air chamber 30.

The control panel 62 is used to operate the mattress temperature controlsystem. In particular, a power button on the control panel 62 is used toswitch on the heater-blower unit 28. After switch on, the heater-blowerunit 28 adopts a standby mode. Pressing the power button again invokesthe run mode, in which the fan 50 starts and thermal control of themattress air chamber 30 is initiated. The control panel 62 is also usedto select a desired temperature of the airflow within the mattress airchamber 30. However, the heater-blower unit 28 may initially operate ata default desired temperature (e.g. a body temperature of 37° C.).

When the heater 52 is in operation, the airflow is heated as it passesthe heater 52. The temperature sensors 54 and 56 sense the temperatureof the local airflows.

The first temperature sensor 54 is arranged to sense the temperature ofa first airflow which passes from the heater 52, along the mattressinlet hose 32 a and into the mattress air chamber 30. In thisembodiment, the first temperature sensor 54 is disposed near the airoutlet 49 a. In particular, the first temperature sensor 54 is disposedwithin the air passageway 48 of the heater-blower unit 28 between theheater 52 and the air outlet 49 a. However, the first temperature sensor54 may alternatively be disposed outside the heater-blower unit 28. Forexample, the first temperature sensor 54 may be disposed at any locationin the first airflow between the heater 52 and the mattress air chamber30 (e.g. at/near either end of the mattress inlet hose 32 a).

The return temperature sensor 56 is arranged to sense the temperature ofa return airflow which passes out of the mattress air chamber 30, alongthe mattress outlet hose 32 b and back into the heater 52. In thisembodiment, the return temperature sensor 56 is disposed near the airinlet 49 b. In particular, the return temperature sensor 56 is disposedwithin the air passageway 48 of the heater-blower unit 28 between theair inlet 49 b and the fan 50. However, the return temperature sensor 56may alternatively be disposed outside the heater-blower unit 28. Forexample, the return temperature sensor 56 may be disposed at anylocation in the return airflow between the mattress air chamber 30 andthe heater 52 (e.g. at/near either end of the mattress outlet hose 32b).

The processor 58 controls the heater 52 based on the airflowtemperatures sensed by both the first and return temperature sensors 54and 56 an based on the desired temperature selected on the control panel62. The processor 58 is operable to switch the heater on to increase theairflow temperature, and the processor is operable to switch the heateroff to reduce the airflow temperature back towards the ambient airtemperature. Thus, the processor 58 is able to control the temperatureof the airflow within the mattress air chamber 30 by means of a simplefeedback system.

The first temperature sensor 54 is a safety temperature limiting sensor.If the temperature of the first airflow deriving from the heater 52exceeds a specified value (e.g. 60° C.), the processor 58 switches offthe heater 52, regardless of the temperature sensed by the returntemperature sensor 56 and regardless of the desired temperature selectedon the control panel 62. The heater 52 is sufficiently powerful to beable to locally heat the surrounding air to a temperature somewhat abovethe specified safety value (e.g. 60° C.). Thus, when the mattress system20 is first switched on, the heater 52 tends to be fairly rapidlyswitched on and off by the processor 58 in response to the temperaturesensed by the first temperature sensor 54. For example, consider asituation in which it is desired to heat the mattress air chamber 30 to37° C. as compared to an ambient air temperature of 20° C. The heater 52will be turned on straight away and very soon the outgoing air in thefirst airflow will reach 60° C. At this stage, the heater 52 will beturned off until the temperature of the first airflow (as sensed by thefirst temperature sensor 54) drops back below 60° C., when the heater 52will be turned back on again, and so on. This rapid switching on and offof the heater 52 in response to the temperature sensed by the firsttemperature sensor 54 continues during the initialization phase of themattress system 20 (i.e. during the period of heating up the mattressair chamber 30 to the desired temperature). After this time, the returntemperature sensor 56 takes a more active role.

The return temperature sensor 56 is the primary temperature sensor formanaging the temperature of the airflow within the mattress air chamber30 during normal operation of the mattress system 20 (i.e. once thedesired temperature within the mattress air chamber has been reached andmust then be maintained). The return temperature sensor 56 measures thetemperature of the return airflow from the mattress air chamber 30. Ifthe sensed return airflow temperature is below a specified value, theprocessor 58 switches on the heater 52. If the sensed return airflowtemperature is above the specified value, the heater 52 is stopped. Thespecified value is related to the desired temperature selected on thecontrol panel 62. Thus, during normal operation of the mattress system20, the heater 52 tends to be switched on and off by the processor 58 inresponse to the temperature sensed by the return temperature sensor 56.Alternatively, rather than constantly switching the heater 52 on and offagain, a variable power heater could be used to control the temperatureof the airflow.

The processor 58 is also operable to control the fan 50. In a preferredembodiment, the fan 50 runs continuously which the mattress system 20 isin operation. Alternatively, the fan 50 may be switched on and off bythe processor 58 and the processor may also vary the fan speed in someapplications. Operation of the fan 50 may depend on the temperaturessensed by both the first and return temperature sensors 54 and 56 and onthe desired temperature selected on the control panel 62 in someapplications.

The pump and control unit 14 of the internal inflatable mattress 10 isindependent of the heater-blower unit 28. However, the pump and controlunit 14 has an air intake on its back face which abuts the heater-blowerunit 28 as shown in FIG. 1. Therefore, in an alternative embodiment, acoupling could be provided between the heater-blower unit 28 and the airintake of the pump and control unit 14 so that temperature-conditionedair is introduced to the inflatable cells 12 of the internal inflatablemattress 10.

Hoses 32 a and 32 b have articulated heater hose couplings at either endfor connection to the mattress 22 and to the heater-blower unit 28.These articulated couplings provide flexibility of the position of themattress 22 with respect to the heater-blower unit 28. In addition, thehoses 32 a and 32 b are insulated to prevent heat loss (or heat gain inthe case of a cooling application rather than a heating application).The heater 52 is able to provide sufficient heat to ensure that themattress air chamber 30 is maintained at a particular temperature,regardless of heat loss between the mattress air outlet 34 b and theheater-blower unit 28. Therefore, insulation of the inlet hose 32 a isgenerally more important than insulation of the outlet hose 32 b.

The elongate mattress 22 of the mattress system 20 will now be describedin more detail with reference to FIG. 4. For clarity, the internalinflatable mattress 10 is shown in FIG. 4, but the associated flexibleconduit 26, hoses 16 and pump and control unit 14 have been omitted. Inaddition, it should be noted that FIG. 4 is intended to be a schematicrepresentation which is not to scale, etc.

In the plan view of FIG. 4, the mattress 22 has four corners 38 a, 38 b,38 c and 38 d. A first longitudinal side 40 a of the mattress 22 extendsbetween the first and second corners 38 a and 38 b. A secondlongitudinal side 40 b of the mattress 22 extends between the third andfourth corners 38 c and 38 d. A first widthwise side 42 a of themattress 22 extends between the first and fourth corners 38 a and 38 d.A second widthwise side 42 b of the mattress 22 extends between thesecond and third corners 38 b and 38 c.

The mattress cover 24 has two apertures in the first widthwise side 42 aof the mattress, the first aperture forming an inlet 34 a to the airchamber 30 and the second aperture forming an outlet 34 b from the airchamber 30. The air chamber inlet 34 a is located near the first corner38 a of the mattress 22. The air chamber outlet 34 b is located near thefourth corner 38 d of the mattress 22. In use, the air chamber inlet 34a is connected to the air outlet 49 a of the heater-blower unit 28 bymeans of the mattress inlet hose 32 a. Similarly, the air chamber outlet34 b is connected to the air inlet 49 b of the heater-blower unit 28 bymeans of the mattress outlet hose 32 b. Thus, air supplied from theheater-blower unit 28 is distributed within the mattress air chamber 30around the outside of the inflatable cells 12 of the internal inflatablemattress 10.

An air inlet conduit 36 a extends within the air chamber 30. The airinlet conduit 36 a extends along a peripheral portion of the mattress 22from the air chamber inlet 34 a. In this embodiment, the air inletconduit 36 a extends along the first longitudinal side 40 a of themattress 22 to the second corner 38 b. The air inlet conduit 36 afurther extends along the second widthwise side 42 b of the mattress 22from the second corner 38 b to the third corner 38 c. The air inletconduit 36 a then partially extends back along the second longitudinalside 40 b of the mattress 22 from the third corner 38 c towards thefourth corner 38 d.

An air outlet conduit 36 b also extends within the air chamber 30. Theair outlet conduit 36 b extends along a peripheral portion of themattress 22 from the air chamber outlet 34 b. In this embodiment, theair outlet conduit 36 b extends approximately one third of the way alongthe second longitudinal side 40 b of the mattress 22 from the airchamber outlet 34 b towards the third corner 38 c of the mattress 22.

The conduits 36 a and 36 b are each formed from a flexible hose or tubein the embodiment of FIGS. 2-4. In alternative embodiments, any form ofconduit suitable for carrying an air supply may be used. For example,the conduits 36 a and 36 b may be rigid or semi-rigid rather thanflexible. Alternatively, the conduits 36 a and 36 b may be formed by theassembly of films or textiles integral to the mattress construction,rather than by discrete hoses.

The air inlet conduit 36 a has a plurality of mutually spaced holes 44 afor introducing the temperature-conditioned airflow from theheater-blower unit 28 into the mattress air chamber 30 at a plurality oflocations. The airflow is depicted schematically by block arrows in FIG.4. As shown in FIG. 4, the holes 44 a are approximately evenly spacedalong the length air inlet conduit 36 a. The majority of the holes aredisposed in a side of the air inlet conduit 36 a so as to direct the airinto the central portion of the air chamber 30 rather than towards themattress cover 34. One of the holes 44 a is the opening at the far endof the hose which forms the air inlet conduit 36 a. The air outletconduit 36 b has two holes 44 b for conveying thetemperature-conditioned airflow out of the mattress air chamber 30. Oneof the holes 44 b is near the air chamber outlet 34 b, and the otherhole is the opening at the far end of the hose which forms the airoutlet conduit 36 b.

In a preferred embodiment, the air inlet conduit 36 a and the holes 44 aare arranged to provide a substantially constant temperaturedistribution of the airflow within the mattress air chamber 30.Alternatively, the air inlet conduit 36 a and the holes 44 a may bearranged to provide a temperature distribution of the airflow within themattress air chamber 30 which varies along the length of the mattress22. For example, it may be desirable to provide an elevated temperaturein the central portion of the mattress air chamber 30 as compared to thetemperature at either end of the mattress air chamber 30. This would actto heat the thorax of a patient on the mattress to a higher temperaturethan their head and feet. Such a temperature distribution may providethe most efficient patient heating in some circumstances.

There are a number of ways of varying the temperature distributionwithin the mattress air chamber 30 by means of the air inlet conduit 36a and the holes 44 a. For example, a greater number of holes 44 a and/orlarger holes 44 a may be provided in the air inlet conduit 36 a in aregion of the mattress air chamber 30 where a relatively hightemperature is required compared to the rest of the mattress air chamber30. Alternatively, the air inlet conduit 36 a may be disposed in adifferent arrangement within the mattress air chamber 30. For example,in one alternative embodiment, the air inlet conduit 36 a may terminateat the second corner 38 a such that it only extends along the firstlongitudinal side 40 a of the mattress 22. This would lead to a reducedtemperature at the far end of the mattress air chamber (i.e. near thesecond and third corners 38 b and 38 c and the second widthwise side ofthe mattress 22) as compared to the arrangement shown in FIG. 4 sinceless warm air would be introduced into the mattress air chamber 30 atthe far end of the mattress air chamber 30 due to the reduced number ofentrance points (i.e. holes 44 a) in that region of the mattress airchamber 30.

Thus, the sizes and locations of the holes 44 a are provided so as toalter the temperature along the length of the mattress 22 depending ontherapy requirements. However, the sizes and locations of the holes 44 aand 44 b may be also optimised to prevent localised heating on theload-bearing surface of the mattress 22 across its width and to preventexcessive back pressure in the blower system.

The mattress cover 24 is formed from a base tray 24 a overlaid by anattached flexible coversheet (not shown). The coversheet is attached tothe base tray 24 a by zips, for example. There are sealed seams toprevent significant leakage of air or fluids. The mattress air chamber30 is therefore substantially closed. The fact that it is only“substantially” closed is related to a number of factors. For example,the coversheet (i.e. the upper surface of the mattress cover 24) is gaspermeable (i.e. breathable), but is liquid impermeable and moistureresistant. Also, the mattress cover 24 is substantially sealed, but notperfectly sealed. For example, the seal may be formed by a zip and anover-flap arrangement. Thus, there is a small amount of natural airaspiration through the mattress cover 24.

The mattress cover 24 is constructed of polyurethane and knitted nylonand is thus stretchable, which helps to ensure that the benefits of adynamic pressure-relieving internal mattress are not lost when used incombination with the heater-blower unit 28.

The lower surface of the mattress (i.e. the surface opposite the upperload-bearing surface) may comprise an insulating layer. For example, aninsulated layer may be permanently fitted to an inner face of a basetray of the mattress 22 to minimize heat loss other than through theload-bearing surface of the mattress 22.

In a preferred embodiment, the mattress 22 is radio-lucent. This isachieved by forming all the components of the mattress 22 (e.g. theinternal mattress 10, the mattress cover 24, the air inlet conduit 36 aand the air outlet conduit 36 b from materials which are radio-lucent(i.e. materials which do not exhibit radio-opacity). This enables anx-ray to be taken of a patient lying on the mattress 22 withoutcompromising the quality of the x-ray picture. The internal inflatablemattress 10 may have a static mode of operation (as opposed to thedynamic pressure-relieving mode of operation described above) to ensurethat there is no movement of the patient during X-ray imaging.

Although the use of an internal mattress 10 in the form of a dynamicpressure-relieving mattress is preferred, it should be noted that thisis not an essential feature of the invention. For example, a more basicinflatable mattress with a single inflation chamber could instead beused. Alternatively, an internal mattress 10 in the form of a sealedfoam mattress could be used. Clearly, the pump and control unit 14 couldbe omitted in these embodiments.

Although preferred embodiments of the invention have been described, itis to be understood that these are by way of example only and thatvarious modifications may be contemplated.

The invention claimed is:
 1. A mattress system comprising: a mattressenclosed by a mattress cover such that a void is created directlybetween the mattress and the mattress cover, the void forming a mattressair chamber; an airflow driving device in fluid communication with themattress air chamber via an air chamber inlet and an air chamber outlet,the airflow driving device being operable to drive a substantiallynon-pressurized airflow through the mattress air chamber around theoutside of the mattress from the air chamber inlet to the air chamberoutlet such that the air flow contacts all exterior sides of themattress and such that a weight of a user on the mattress system iswholly supported by the mattress rather than by either the mattress airchamber or the substantially non-pressurized airflow through themattress air chamber; a heat adjustment unit for heating or cooling theairflow so as to control a temperature of the airflow within themattress air chamber; and a return temperature sensor arranged to sensea temperature of a return airflow from the air chamber outlet to theheat adjustment unit.
 2. The mattress system of claim 1 furthercomprising an air inlet conduit extending within the mattress airchamber from the air chamber inlet, the air inlet conduit comprising aplurality of mutually spaced holes for introducing thetemperature-controlled airflow into the mattress air chamber at aplurality of locations.
 3. The mattress system of claim 2 wherein theair inlet conduit and the holes are arranged to provide a substantiallyconstant temperature distribution of the airflow within the mattress airchamber.
 4. The mattress system of claim 2 wherein the mattress iselongate and the air inlet conduit and the holes are arranged to providea temperature distribution of the airflow within the mattress airchamber which varies along the length of the mattress.
 5. The mattresssystem of claim 2 wherein the mattress is elongate and the air chamberinlet is located at or near a first corner of the mattress such that theair inlet conduit extends along a longitudinal edge of the mattresstowards a second corner of the mattress.
 6. The mattress system of claim5 wherein the air inlet conduit further extends from the second cornerof the mattress along a widthwise edge of the mattress towards a thirdcorner of the mattress and then partially extends back along an oppositelongitudinal edge of the mattress towards a fourth corner of themattress.
 7. The mattress system of claim 1 further comprising atemperature sensor arranged to sense a temperature of the airflow. 8.The mattress system of claim 7 wherein the temperature sensor comprisesa first temperature sensor arranged to sense a temperature of a firstairflow from the heat adjustment unit to the air chamber inlet.
 9. Themattress system of claim 7 further comprising a processor operable tocontrol the heat adjustment unit based on the sensed airflowtemperature.
 10. The mattress system of claim 9 further comprising meansfor selecting a desired temperature distribution of the airflow withinthe mattress air chamber, the processor further being operable tocontrol the heat adjustment unit based on the selected temperaturedistribution.
 11. The mattress system of claim 1 wherein the mattresshas a load-bearing upper surface for receiving a load, and the lowersurface of the mattress comprises an insulating layer.
 12. The mattresssystem of claim 1 wherein the mattress is radiolucent.
 13. A mattresssystem comprising: a mattress enclosed by a mattress cover such that avoid is created directly between the mattress and the mattress cover,the void forming a mattress air chamber; an airflow driving device influid communication with the mattress air chamber via an air chamberinlet and an air chamber outlet, the airflow driving device beingoperable to drive a substantially non-pressurized airflow through themattress air chamber around the outside of the mattress from the airchamber inlet to the air chamber outlet such that the air flow contactsall exterior sides of the mattress and such that a weight of a user onthe mattress system is wholly supported by the mattress rather than byeither the mattress air chamber or the substantially non-pressurizedairflow through the mattress air chamber; a heat adjustment unit forheating or cooling the airflow so as to control a temperature of theairflow within the mattress air chamber; and an air outlet conduitextending within the mattress air chamber to the air chamber outlet, theair outlet conduit comprising at least one hole for conveying thetemperature-controlled airflow out of the mattress air chamber.
 14. Themattress system of claim 13 wherein the mattress is elongate havingfirst, second, third, and fourth corners, and wherein the air chamberoutlet is located adjacent the fourth corner of the mattress and the airoutlet conduit extends approximately one third of the way along alongitudinal edge of the mattress towards the third corner of themattress.
 15. A mattress system comprising: an inflatable mattressenclosed by a mattress cover such that a void is created directlybetween the inflatable mattress and the mattress cover, the void forminga mattress air chamber; an airflow driving device in fluid communicationwith the mattress air chamber via an air chamber inlet and an airchamber outlet, the airflow driving device being operable to drive asubstantially non-pressurized airflow through the mattress air chamberaround the outside of the mattress from the air chamber inlet to the airchamber outlet such that the air flow contacts all exterior sides of themattress; and a heat adjustment unit for heating or cooling the airflowso as to control a temperature of the airflow within the mattress airchamber; wherein the inflatable mattress comprises at least two separateinflation chambers that are inflatable independently of one another to adesired inflation pressure, and wherein the inflatable mattress isindependent of the airflow driving device in fluid communication withthe mattress air chamber such that a weight of a user on the mattresssystem is wholly supported by the inflatable mattress rather than byeither the mattress air chamber or the substantially non-pressurizedairflow through the mattress air chamber.
 16. The mattress system ofclaim 15 wherein each inflation chamber comprises a respective pluralityof mutually spaced inflatable cells.
 17. The mattress system of claim 15further comprising a pump and a control system operable to independentlyvary the inflation pressure of each inflation chamber over time.